1. Field of the Invention
The present invention relates to a semiconductor device and a method of forming the same, and more particular, to a semiconductor device for electrostatic discharge protection and a method of forming the same.
2. Description of the Prior Art
Electrostatic discharge (ESD) is a transient process of high energy transformation from external to internal of an integrated circuit (IC), which may temporarily disable or permanently destroy the electronic systems, thereby adversely damaging to the ICs. Therefore, an ESD protection device is designed to provide a discharge path and to protect the ICs from being blown out by instantaneous discharge currents.
Current ESD protection device includes a bipolar transistor (BJT) formed by a source region, a drain region and an anti-type doped well disposed in a substrate, and which is usually surrounded by a guard ring. However, due to the structural arrangement according to the practical requirements, diverse distances may be formed between different parts of the drain region and the guard ring. Since MM (machine model) ESD waveform consists of both positive and negative sinusoidal peaks that decay exponentially, more charges may accumulate at the parts of the drain region which is relatively closer to the guard ring during the first negative peak. Accordingly, during the positive peak next to the first negative peak, the parts of the drain region relatively closer to the guard ring are turned on faster than the other parts of the drain region, thereby resulting in non-uniform turn on issue. Thus, these parts of the drain region closer to the guard ring are easily damaged due to such non-uniform turn on issue. Hence, how to improve current ESD protection device has become an important task in this field.